The local structure of the interlamellar lanthanide ions in montmorill
onite upon heating is studied. The analysis of the EXAFS data has been
carried out using two model environments, that of La3+ aquocomplex an
d that of the lanthanum oxide. The information thus obtained is crucia
l in elucidating the intercalation mechanism and demonstrates the impo
rtant role that XAFS techniques can play in the knowledge of the locat
ion and environment of the exchangable ions in layered silicates.